Electric arc lamp



H. L. THOMAS ELECTRC. ARG LAMP May 12, 1936.

Filed Jan. 5, 1935 3 Sheets-Sheet l Ffg. m

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#Zwin ELECTRICARC LAMP Filed Jan. 5, 1935 5 Sheets-Sheet 2 AA-UAM May H2? B936. H. L. THOMAS ELECTRIC ARC LAMP 3 Sheets-Sheet 3 Filed Jan. 5, 1955 nm E 7H JW Patented May 12, 1936 UNITED STATES PATENT GFFICE to Sperry Gyroscope Company Inc., Brooklyn,

N. Y., a company of New York Application January 3, 1935, Serial No. 195

In Great Britain January 4, 1934 8 Claims.

I'his invention relates to electric arc lamps in which the position of the negative electrode is automatically controlled to maintain a proper length of arc according to the voltage across the arc itself. In the operation of such lamps, switching off the current causes the voltage across the arc gap to drop to zero, and in consequence, unless the control mechanism is thrown out of action immediately, the negative electrode will be retracted beyond the normal working position. In any case, when the lamp is extinguished, the gap left between the electrode is liable to be greater than the normal.

The chief object of the present invention is to obviate the above-mentioned disadvantages and with this object in view the invention may be stated broadly as consisting in the provision of means for causing the arc to be quickly struck when the current is first switched on by advancing the negative electrode substantially instantaneously to touch the positive electrode and then quickly detracting it to draw out the arc to the proper burning length.

More specifically stated as applied to a specific embodiment the invention consists inV giving a temporarily accelerated advance of the negative electrode immediately the current is switched on and before the arc is struck, but in causing the additional striking means to be rendered inoperative immediately the arc has been struck.

According to one construction the negative electrode holder and the feed screw therefor are given an initial rapid bodily movement towards the positive carbon without disturbing the feed 35 screw mechanism and, as soon as the electrodes touch, the negative electrode with its holder and feed screw retreats to the proper arcing distance and the feed screw mechanism then operates normally. Alternatively, the bodily movement of 10 the negative electrode is effected by mounting the negative electrode and its holder as a unit on a movable portion of the supporting bracket and in moving said movable bracket portion.

For convenience of description the invention will be described more fully with reference to the construction of arc lamp described and shown in the prior United States patent specification No. 1,761,668.

In the accompanying drawings, Figure 1 is a part-,sectional side elevation of an electric arc lamp embodying the essential features of the present invention in one constructional form, and Figure 2 is a plan View of the underside of the lamp looking upwards. Figure 3 is an enlarged elevational view of a portion of the base of the lamp and of the linkage carried thereby, and Figure 4 is a corresponding plan View. Figure'5 is an elevation of an alternative construction.

In its general arrangement the lamp illustrated is similar to that described and illustrated 5 .in the specification of the prior Patent No. 1,761,668. It comprises a base I0 supporting brackets II and I2 upon which are mounted the positive and negative heads respectively. The driving mechanism for 'feeding and rotating the 10 electrodes comprises a motor operating through links I9 and 20 to drive a disc 25 (see Figure 2) carrying a crank pin 26. Said crank pin engages a U -shaped slot 2l' formed in a reciprocating member 28, comprising a shaft portion 29 operating 15 in fixed guides 36 and 3| to constrain the motion of said member 28 to lateral reciprocatory motion in a straight line.

The reciprocating member 28 has pivoted thereto at 32 a pawl 33 adapted to engage a ratchet 2,0 34 each time the reciprocating member 28 moves toward the right in Figure 2. The rotation of ratchet 313 will cause rotation of shaft 35 to which it is connected, said shaft 35 having a gear 36 at its upper end meshing with a gear 31 at one 25 end of the sleeve which is supported in fixed hub 36. Said sleeve has fixed thereto at its other end beyond hub 38 a bracket 46, upon which is fixed or supported the entire positive electrode rotating and feeding mechanism so that as the ratchet 30 35i is rotated, bracket 46 will be rotated to cause rotation and feeding of the positive electrode.

The negative electrode N is adapted to be clamped in a holder lil, mounted upon a carriage 'II through which extends loosely, without thread- 35 ed engagement therewith, a feed screw 12. Engagement between the screw shaft I2 and the electrode is effected by means of a linger (not shown) extending from the clamp 'I0 and engaging between adjacent threads of the screw 12. 40 Rotation of the entire carriage andr electrodeis prevented by means of a tongue 'I6 extending downwardly from the carriage 'II and engaging in a slot within bracket I2.

The feeding' of` the negative electrode is, 45 of course, accomplished by rotating the feed screw 12 in one direction or the other which causes cor'- responding feeding or retractive movement of the electrode. Rotation of shaft 12 in one direction or the other is accomplished by means such as gear 80, fixed at one end to the shaft "I2, meshing with gear 8l on the upper end of a shaft 82 extending through base I0 and having a pair of ratchet wheels 83-84 at its lower end. Said ratchet wheels have theirv teeth oppositely disposed and are adapted to be engaged by pawls 85-86, respectively, each pivotally mounted on a bracket 8l carried at the end of the reciprocatory member 28. A spring 88 normally presses said pawls into engagement with their respective ratchet wheels so that each time reciprocatory member 28 moves toward the left (in Figure 2) said pawls would ordinarily engage their ratchets to operate the negative electrode one in one direction and the other in the other direction. Obviously it is desired to have only that pawl in engagement with its respective ratchet as is necessary to advance or retract the negative electrode depending upon the length of arc. For this purpose there is provided the guide member 90 interposed between pawls 85 and 36 and fixed to one end of a bell crank 9| whose other arm 92 forms the armature of the voltage coil 93.

Spring 94 retracts this armature when no current is passing through the voltage coil 93 and in that condition guide 90 holds the pawl 85 out of engagement with its respective ratchet (Figure 2) but permits pawl 86 to engage its ratchet and actuate it in a direction to feed the negative electrode backward at each stroke. When, however, the voltage coil 93 is fully excited it overcomes spring 94 so that guide 90 allows pawl 85 to engage its ratchet wheel and feed the negative electrode forward while pawl 86 is held clear of its ratchet wheel. When the arc is burning with its proper length the coil 93 receives a voltage proportional to the difference of potential between the two ends of the arc, and spring 94 is adjusted sc that in these conditions it just balances the pull of the coil when guide 90 is in the intermediate position where neither pawl 85 nor 86 can engage its ratchet. If the arc burns too long the voltage across the arc increases so that the pull of coil 93 overcomes spring 94 thereby moving guide 90 so that pawl 35 feeds the negative electrode forward and shortens the arc. Conversely, if the arc is too short, the arc voltage is reduced, spring 94 is stronger than the pull of coil 93, and pawl 86 comes into engagement to retract the negative electrode. The length of arc at which the retraction of the negative electrode begins may be varied by varying the tension of spring 94.

The above described general features of the arc lamp illustrated are known and the essential feature of the present invention as applied to this lamp consists in imparting a rapid bodily advance movement to the electrode holder and feed screw when starting up the lamp as will now be explained. Formed on or secured to the external face of the pawl 86 is a projection 95, and attached to the base I of the lamp is a linkwork comprising a lever 96 the tail of which is adapted to be engaged by the aforesaid projection 95. Another limb of the linkwork is the arm 91 having a cup-shaped end 98 for seating the lower end of the feed screw 12 which extends through and beyond the gear 80 and is longitudinally slidable y through said gear wheel but keyed thereto so as to be rotated thereby.

When the lamp is switched oif the negative electrode N usually retracts to a greater distance than the normal arc length because the driving motor continues to run for a short time after the current has been disconnected and while pawl 86 is consequently operating on its ratchet. The next time the lamp is switched on therefore it is necessary to advance the negative to touch the positive electrode before the arc can be struck. It has hitherto been the practice to rely on pawl 85 Aamd-iii to effect this advancing by the method described above. Prior to the arc being struck the potential difference between the two electrodes is a maximum and consequently armature 92 is strongly attracted by voltage coil 93, and pawl 85 is therefore brought into engagement with its ratchet. Under these conditions several strokes of the reciprocating rod 28 are generally necessary before the negative is fed up to strike the are, and consequently seconds or longer time may elapse between the instant of switching on and the lighting of the lamp. In the present invention this time of striking is reduced by the operation of the projection 95 on the back of pawl 86. Under the conditions of maximum voltage when armature 92 is pulled as close as possible to the end of the core of voltage coil 93, guide 90 moves over so far that pawl 86 is not only taken clear of engagement with its ratchet wheel but projection 95 can engage the tail of a lever 96-(see Figure 3) Then as the projection is moved to the left by the action of rod 28, lever 96 is thereby rocked over and serves, through the connecting link and lever 91, to raise the screw 12 bodily and advances the negative electrode to an extent equal to the normal arc gap.

At the same time the pawl 85 operates to give an additional forward movement to the negative electrode. The crank pin 26 then shifts the pawls to the right in Figure 2, thus removing projection 95 (on pawl 86) out of engagement with the tail of lever 96 thereby allowing the linkage to rock under the weight of the negative electrode and its associated parts assisted by the spring 99. Hence the arc will be drawn out to approximately its normal burning length. The voltage across the voltage coil will then become approximately normal, and the guide piece 98 will be returned to its usual working position and the length of the arc will subsequently be maintained in the usual Way.

It is to be understood that the position of the linkage is such that the projection 95 on the pawl 86 can only engage the tail of the lever 96 of the linkwork when the full voltage exists between the two electrodes, and this can only occur when the lamp is connected across the normal source of the electric current and the arc is not struck. In other words, when the arc has been established, the pawl 86 during its reciprocations to feed the negative electrode forwards gradually in the normal manner is' out of reach of the tail of the lever 96.

In some constructions of arc lamp the negative electrode may not be fed by a feed screw as above described, but be driven forward by knurled rollers mounted in a bracket which carries the negative mechanism. In such construc- Cil tion it is not practicable to advance the negative electrode by advancing a screw in the manner above described, but the bracket I2 carrying the negative electrode the holder and the feed screw can be hinged as shown in Figure 5 about a horizontal pivot |00 in such a way that the bracket can be swung up to bring the negative electrode against the nose of the positive electrode. In this case the lever 96 actuated as above described operates by swinging the hinged bracket portion into the striking position. For this purpose the lever 96 is shown attached at its upper end to a link |0I connected to the lower end of a lever |02 the upper end of which is forked to engage a pin |03 on the foot |04 of the bracket I2. It may be noted that the gear wheel 80 will move with the bracket away from the gear wheel 8| but will return into meshing relation thereto as the bracket returns to its normal position. In any case it should be noted that when the pawl 86 during oscillation has made an excursion in the direction to push the lever, its return excursion will allow the negative electrode to 'come back to its previous position either by its own weight or under the action of a spring provided for the purpose. If the arc has been struck this retreating movement will assist in drawing it out to the right length. If, on the other hand, the forward stroke was insufficient to bring the electrodes into contact, the operation would be repeated on the next forward excursion of the pawl with the advantage that meantime the gap to be closed will be reduced by the operation of the pawl on the ratchet wheels.

In effect, therefore, the above described arrangements give a temporarily accelerated advance of the negative electrode immediately the current is switched on and before the arc is struck, but once the arc has been struck and the guide piece 90 has been lifted from its lowest position, the means for giving the rapid striking motion which are now no longer necessary are cut out of action because the above-described projection 95 on the pawl 86 is lifted clear of the tail of the level S6 with which it has to engage.

What I claim iszl. An electric arc lamp comprising positive and negative electrodes, a voltage coil, and feed means controlled thereby for automatically feeding the negative electrode, in combination with lever means for giving temporarily an accelerated advance movement to the negative electrode when the current is switched an and before the arc is struck, said lever means becoming inoperative immediately after the arc has been struck.

2. An electric arc lamp` comprising positive and negative electrodes, a voltage coil, and screw feed means controlled thereby for automatically feeding the negative electrode, in combination with lever means whereby before the arc is' struck the switching on of the current causes the voltage coil to operate through said lever means to give the negative electrode a rapid closing movement to strike the arc, whereupon the electrode retreats to the correct arcing distance and is subject to normal feeding.

3. An electric arc lamp comprising positive and negative electrodes, a voltage coil, a movable negative electrode holder, a feed screw therefor, and means controlled by said voltage coil to actuate said feed screw, in combination with additional means actuated by the voltage coil when the current is switched on but the arc is not struck to give a rapid advance movement to said electrode holder and feed screw without rendering the normal feeding inoperative.

4. An electric arc lamp comprising positive and negative electrodes, a voltage coil, a movable negative electrode holder, a. feed screw therefor, and means controlled by said voltage coil to actuate said feed screw, a movable bracket carrying said electrode, and electrode holder, and means actuated by said voltage coil when the current is switched on but the arc is not struck for giving a rapid bodily advance movement to said bracket with its electrode and holder suiiicient to close the gap, whereupon said rapid advance means become inoperative.

5. A method of striking the arc of an electric arc lamp of the kind in which the position of the negative electrode is automatically controlled to maintain a proper length of arc according to the voltage across the arc itself, which consists in causing the electric current when switched on to impart to the negative electrode a rapid plain closing movement with respect to the positive electrode and thereupon cease to maintain the advanced position of the negative electrode and leave it to the normal automatic control means.

6. An electric arc lamp comprising positive and negative electrodes, a voltage coil, an armature movable by said coil, .an adjustable spring acting on said armature oppositely to said coil, ratchet and pawl mechanism actuated by said armature for feeding the negative electrode forwards and backwards to maintain the arc, and means actuated by the forward feeding pawl when the current is switched on but the arc is not struck to impart a rapid closing movement of the negative electrode with respect to the positive electrode.

'7. An electric arc lamp according to claim 6, the forward feeding pawl carrying a projection which actuates the means for giving the rapid closing movement to the negative electrode.

8. An electric arc lamp according to claim 6, including a linkwork, and a projection on the negative feeding pawl to rock said linkwork and thereby give the negative electrode the rapid advance.

HAROLD LESLIE THOMAS. 

